η′ and η mesons with connection to anomalous glue

A review of the present understanding of eta' and eta meson physics and these mesons as a probe of gluon dynamics in low-energy QCD is presented. Recent highlights include the production mechanism of eta and eta' mesons in proton-nucleon collisions from threshold to high energy, the eta' effective mass shift in the nuclear medium, searches for possible eta and eta' bound states in nuclei, as well as precision measurements of eta decays as a probe of light-quark masses. Recent experimental data, theoretical interpretation of the different measurements, and the open questions and challenges for future investigation are discussed.